Method of making thin film structure of metal

ABSTRACT

A method of making an electron-beam permeable thin film of metal for use as a window of an electronic recording tube whose interior must be maintained at a high vacuum, so as to obtain a thin film structure which does not permit infiltration of gas into the tube and fully maintains the desired high vacuum within the tube.

United States Patent 1 3,607,676

[72] Inventors Yoshihiro Uno [50] Field of Search 204/12, 13, Machida-shi; 192 Hidehiko Kawakami, Kawasaki-shi, both of Japan References Cited [21] Appl. No. 776,707 UNlTED STATES PATENTS [2 1 Filed 3 3,203,876 8/1965 Deyrup 204/13 [45] Patented Sept. 21, 1 [73] Assignee Matsushita Electric Industrial Co., Ltd. FOREIGN I )A TENTS Osaka Japan 275,221 7/1927 Great Britain 204/12 i y Nov. 27, D 27 Great Britain [33] Japan Primary ExaminerJohn Hv Mack [31] 42/76670 and 43/215 Assistant Examiner-Sidney S. Kanter A1l0rneyStevens, Davis, Miller & Mosher [54] METHOD OF MAKING THIN FILM STRUCTURE ABSTRACT: A method of making an electron-beam permeagg r gii g Figs. ble thin film of metal for use as a windovv of an electronic recording tube whose interior must be maintained at a high [52] U.S.C| 204/12, vacuum 50 as to obtain a thin film structure which does not 204/192 permit infiltration of gas into the tube and fully maintains the [51] Int. Cl C231) 7/02 desired high vacuum within the tube,

PATENTEUSEP21 I971 3507.676

INVENTQRS OSHIHIRO LLAIO lube HIIrO mun/mm 2%. I BY f ATTORNEYS METHOD OF MAKING THIN FILM STRUCTURE OF METAL This invention relates to an electron-beam permeable thin film for use as a window of an electronic recording tube whose interior must be maintained at a high vacuum, and more particularly to a method of making a thin film structure of metal which does not permit infiltration of gas and other fluid into the tube thereby fully maintaining the desired high vacuum within the tube.

Metals, ceramics and glass are common materials which are employed for the vacuum sealing of conventional electronic tubes within which a high vacuum must be maintained. In a device such as an electronic recording tube having a window in the form of an electron-beam permeable thin film, the thin film isolating a high vacuum atmosphere from a low vacuum atmosphere such as atmospheric air must not permit undesirable infiltration of gas therethrough into the internal atmosphere which must be maintained at a high vacuum. When, however, metals of some kind are used to make the electronbeam permeable window, the thin film made from these metals can not prevent infiltration into the tube of molecules of gases having a small molecular weight such as hydrogen gas and helium gas. This is objectionable since the vacuum within the tube may thereby be lowered to an extent that the tube can not properly function as a recording tube. For example, when the electron-beam permeable window is made by a physical or chemical method such as evaporation or electrodeposition, a defect such as pinholes of very minute area may be formed in the window in the course of manufacture thereof, and because of the presence of the defect, it is hardly possible to prevent infiltration of gas from a low vacuum atmosphere such as the atmospheric air into the tube whose interior is kept at a high vacuum.

It is therefore a primary object of the present invention to provide a method of making a thin film structure for use an an electron-beam permeable window of an electronic recording tube, which thin film structure includes a means for preventing an undesirable reduction in the vacuum within the tube even if permeation of such as hydrogen or helium gas through the thin film should occur or pinholes giving rise to infiltration of gas might exist within the thin film, thereby maintaining a high vacuum within the tube so that the tube can properly function.

The above and other objects, features and advantages of the present invention will be apparent from the following description taken in conjunction with the corresponding drawings, in which:

FIG. 1 is a schematic sectional view showing the method of making a thin film structure according to the present invention;

FIG. 2 is a schematic sectional view of a thin film device including the thin film structure shown in FIG. 1;

FIG. 3 is a schematic sectional view of part of an electronic recording tube having an electron-beam permeable window made according to the present invention; and

FIG. 4 is a schematic sectional view showing the step of evacuation as by a rotary pump.

Referring to FIG. 1, a thin film of metal 2 is deposited as by vacuum evaporation or sputtering on a sufficiently cleaned smooth surface of a glass substrate 1. Known methods, other than the above-mentioned vacuum evaporation or sputtering, for depositing a thin metallic film on the surface ofa substrate include thermal decomposition, reaction in gaseous phase and chemical plating. Of such known methods, thermal decomposition and reaction in gaseous phase have disadvantages in that the thin film formed does not have sufficient adhesiveness to the substrate and the control of the thickness of the film is difficult and further bulky equipment is required for the process. Chemical plating also has a drawback in that it is difficult to form a smooth film free of pinholes over the entire surface of the substrate. Further the film formed by chemical plating is not sufficiently pure and is apt to become an alloy. On the contrary, vacuum evaporation or sputtering provides a smooth, dense and holeless film well controlled in the thickness.

The metal forming the thin film 2 has preferably an ionization tendency which is equal to or less than that of a metal used in plating described later. The vacuum evaporation, when employed, is preferably carried out at a sufficiently slow rate.'While the vacuum evaporation gives a sufiicient bond between the metal film 2 and the glass substrate 1, a further stronger bond can be obtained when the sputtering is resorted to. The metal forming the layer 2 may be nickel, for example, when the thin film to be finally obtained is of nickel. After the thin film 2 has been formed on the glass substrate 1, the vacuum is broken and the thin film 2 is exposed to the atmospheric air for a certain period of time which may be several minutes. Then, the sample is replaced in the vacuum evaporation apparatus and a thin film of metal 3 is formed on the thin film 2 by vacuum evaporation. The metal 3 is preferably a chemically stable metal such as gold, silver or platinum. Then, nickel plating is performed employing the thin film 3 as an electrode thereby to form a nickel layer 4 of predetermined thickness on the thin film 3. At the completion of the plating step, the stack is sufficiently cleansed and dried, and then the thin film structure is stripped off from the glass substrate 1. The stripping occurs at the interface of the thin films 2 and 3, that is, between the surface of nickel exposed to the air and the surface of gold or like metal. The bond between the thin films 2 and 3 has an ideal property which is required for the successful manufacture of the thin film structure. More precisely, the bonding force between these films is sufficiently strong to withstand the tendency toward stripping during the plating operation and is such that no damage is imparted to the thin film 3 during the stripping operation or the thin film 4 is not stripped off from the thin film 3.

FIG. 2 shows one form of a thin film device including the thin film structure obtained in this manner. The thin film device shown in FIG. 2 comprises a mesh member of nickel to one surface of which the thin film structure is attached. The device is used as the faceplate of a cathode-ray tube which is adapted to lead an electron-beam out of the vacuum into the atmospheric air for the sake of recording.

In FIG. 2, a layer 5 of electrical insulator is formed on a thin film 4 made by the method shown in FIG. I. The layer 5 may be formed by the photoresist technique or evaporation of an electrical insulator. Then, nickel is plated again to allow growth of a nickel layer 6 at those portions at which the electrical insulator is not disposed. Thus, the nickel layers 4 and 6 are integrally combined together. The stack of the thin films is split at the interface of the thin films 2 and 3 as FIG. I, and the electrical insulator 5 is removed to obtain a thin film device in which the thin film structure is backed up by the perforated support 6.

It will be understood that the method according to the present invention comprises forming a first layer of a metal on a smooth surface of a base, exposing the first metal layer to the atmospheric air or any other suitable gas, depositing a chemically stable metal on the exposed surface of the first metal layer by evaporation to form a second layer thereon, then depositing a thin film of a metal on the second metal layer by evaporation or plating, and splitting the stack at the interface of said first metal layer and said second metal layer. Thus, the thin film structure of very thin and uniform nature can be separated from the base.

The thin film device made by the above method may include very minute pinholes because foreign matter such as dust and dirt principally giving rise to objectionable pinholes might electrostatically attach to the base during vacuum evaporation. A thin film device including therein the pinholes can not be used as a vacuum sealing window for an electronic recording tube.

The present invention contemplates further the provision of an additional means for application to the thin film device having very minute pinholes therein so that the thin film device can fully serve the purpose of vacuum sealing of the interior of an electronic tube. By virtue of the provision of the additional means, the thin film device can be manufactured at a remarkably improved yield rate.

Referring to FIG. 3, a support 8 having a split 8 is bonded to a glass envelope 7 of an electronic tube by a layer 9 of a suitable binder. An electron-beam permeable window 11 of thin film structure as described above is disposed opposite to the slit 8' and is held by a reinforcing member 10 which is bonded to the support 8 by a binder layer 12. A layer of highmolecular material 13 such as an epoxy resin is coated on the inner surface of the thin film structure 11 forming the electron-beam transmissive window. That is, a gas permeation preventive layer of a material, for example, a high-molecular material such as silicone resin or epoxy resin is thinly coated on the inner surface of the thin film structure 11 for preventing infiltration of gas into the electronic tube and maintaining a high vacuum within the electronic tube. Then, as shown in FIG. 4, means such as a rotary pump is used to apply suction to the thin film structure 11 on the side at which the resin layer 13 is not disposed. As a result, the resin 13 fills the pinholes and any other minute pores within the thin film structure 11 thereby inhibiting objectionable infiltration of gas into the glass envelope through the thin film structure 11. The layer 13 may then be wiped away by use of a suitable solvent. The resin layer 13 may remain in a thickness of the order of 0.5 micron because the resin has a relatively small molecular weight in view of the fact that its components are silicone, oxygen and hydrogen and the resin of such a nature and of such a small thickness does not in any way spoil the electron-beam permeating function of the thin film structure 11. Furthermore, such a resin layer has a great ability to stop the infiltration of hydrogen gas and the like therethrough. An evaporated film of metal such as aluminum may additionally be deposited on the thinly coated high-molecular material layer in order to avoid accumulation of a charge on the dielectric.

it will be appreciated from the foregoing description that the present invention provides a thin film device in which a resin layer is coated on an electron-beam permeable thin film structure separating the interior of an electronic tube from the exterior thereof. Thus, any deterioration of the high vacuum within the tube due to infiltration of gas molecules through the thin film structure can not occur even if the thin film structure contains pinholes and other defects therein.

We claim:

1. A method of making a thin film of metal used for an electron-beam permeable window of an electronic recording tube, the interior of which is maintained at high vacuum; said method comprising the steps of forming a first layer of nickel by vacuum evaporation or sputtering on a smooth surface of a flat, substrate, exposing said first layer of nickel to an oxidative atmosphere,

depositing a thin layer of a metal selected from the group consisting of gold, silver and platinum by vacuumevaporation on the exposed surface of said first layer to form a second layer of metal thereon,

depositing a film of nickel by electroplating on said second layer, and

stripping off the top layers at the interface between said first and second layers to form said thin film from said top layers.

2. A method according to claim I wherein said flat substrate is a glass substrate.

3. A method of making a thin structure used for an electronbeam permeable window, said thin structure consisting of a thin film reinforced with a perforated support, said method comprising the steps of forming a first layer of nickel by vacuum evaporation or sputtering on a smooth surface of a flat, substrate, exposing said first layer of nickel to an oxidative atmosphere,

depositing a thin layer of a metal selected from the group consistin of gold, silver and platinum by vacuum evaporation on the exposed surface of said first layer to form a second layer of metal thereon,

depositing a film of nickel by electroplating on said second layer to form a third layer,

depositing a layer of insulating material on said third layer leaving an uncoated area,

further depositing nickel on said uncoated area to form said perforated structure,

stripping off said thin structure consisting of the top layers at the interface between said first and second layers.

4. A method according to claim 3 wherein said fiat substrate is a glass substrate. 

2. A method according to claim 1 wherein said flat substrate is a glass substrate.
 3. A method of making a thin structure used for an electron-beam permeable window, said thin structure consisting of a thin film reinforced with a perforated support, said method comprising the steps of forming a first layer of nickel by vacuum evaporation or sputtering on a smooth surface of a flat, substrate, exposing said first layer of nickel to an oxidative atmosphere, depositing a thin layer of a metal selected from the group consisting of gold, silver and platinum by vacuum evaporation on the exposed surface of said first layer to form a second layer of metal thereon, depositing a film of nickel by electroplating on said second layer to form a third layer, depositing a layer of insulating material on said third layer leaving an uncoated area, further depositing nickel on said uncoated area to form said perforated structure, stripping off said thin structure consisting of the top layers at the interface between said first and second layers.
 4. A method according to claim 3 wherein said flat substrate is a glass substrate. 